OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 in tensile strength for the Al7075 nanocomposite when reinforced beyond 2% SiC with a constant 1% graphene proportion may be attributed to increased brittleness in the nanocomposite, resulting from stress concentrations caused by the SiC particles. This study underscores the importance of balancing hardness and tensile strength in nanocomposites to achieve the desired properties, highlighting the need for careful consideration of reinforcement material selection. It is crucial for researchers to carefully optimize reinforcement percentages to balance strength and hardness in Al7075-based nanocomposites. When properly combined, graphene and silicon carbide reinforcements can synergistically enhance mechanical properties. This study indicates that Specimen 7, composed of Al7075, 0.5% graphene, and 3% SiC, exhibits an excellent balance between tensile strength (156.62 MPa) and hardness (155.52 BHN), representing an optimal combination of these characteristics. The enhanced mechanical strength resulting from the addition of SiC and graphene to the Al7075-T6 nanocomposite may be attributed to SiC’s hardness and modulus, which facilitate load transfer, grain refinement, and dislocation impediment. Furthermore, graphene’s high tensile strength and large surface area improve interfacial bonding and inhibit cracking. Differential thermal expansion between the reinforcements and the matrix generates dislocation networks that impede plastic deformation. Consequently, SiC and graphene enhance the composite’s tensile strength, hardness, and wear resistance. The test results demonstrate that the hybrid nanocomposites possess higher tensile strength and hardness than the unreinforced Al7075 alloy, and these properties increase with the hybrid reinforcement ratio. The correlation between mechanical properties and the homogeneous dispersion of nano reinforcements, which inhibits dislocation movement, reduces porosity, and minimizes nanoparticle agglomeration, is explored in the subsequent subsection focusing on the microstructural and fracture surface analysis of Al7075-based nanocomposites. The microstructural and fracture surface analysis of nanocomposites The superior tensile strength (156.62 MPa) and hardness (155.52 BHN) observed for Specimen 7 among the prepared nanocomposites can be elucidated through microstructural and fracture surface analysis. Fig. 3 presents SEM images of the fracture surfaces of Specimen 7 (Al7075 + 0.5% Gr + 3% SiC) after tensile testing. Figs. 3, a through 3, d display SEM images of the fracture surfaces at increasing magnification levels. These images reveal the microstructural traits and features of the fracture surfaces at various scales. The SEM analysis provides valuable insights into the material’s failure mechanisms and fracture propagation characteristics. A dense, dimpled surface with homogeneous microvoids and minimal particle pull-out is observed, indicative of ductile fracture with strong matrix-reinforcement bonding and efficient load transfer. The presence of fine, uniformly distributed dimples suggests that SiC particles served as solidification nucleation sites, while graphene blunted crack tips and impeded dislocation movement. SEM images of the fracture surfaces of Specimen 8 (Al7075 + 1% Gr + 2% SiC) are shown in Figs. 4, a through 4, d at increasing magnification levels. The fracture surfaces exhibit non-uniform dimples with mixed-mode characteristics, indicating interfacial decohesion and reinforcement particle pull-out. Increased graphene concentration may weaken matrix-reinforcement bonding due to graphene agglomeration and reduced wettability. Stress concentrations caused by microstructural discontinuities can lead to premature cracking, potentially explaining why Specimen 8 exhibits lower tensile strength and hardness compared to Specimen 7 despite having a higher overall reinforcement content. This study observed that Al7075 nanocomposites prepared with stirring exhibit a more uniform and homogeneous surface compared to those prepared without stirring. Scanning electron micrographs reveal distinct surfacemorphologies for composites preparedwith andwithout stirring. Fig. 5, a depicts the unstirred composite’s flat, featureless surface characterized by scattered particles, non-uniform reinforcement distribution, and agglomerates. This non-uniformity indicates inadequate matrix-reinforcement particle dispersion resulting from insufficient mechanical mixing during fabrication. Visible voids and poor interfacial bonding suggest weak matrix-reinforcement interaction, which can negatively impact composite mechanical performance. Fig. 5, b displays the stirred composite’s smooth, homogeneous surface. Visible striations and consistent fine particle dispersion suggest that stirring enhances mixing and reinforcement
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